What was found
CENTER AUTOPILOT DISCONNECTED APPROXIMATELY 1.5 HRS IN CRUISE FLIGHT. THIS WAS FOLLOWED BY NO-LAND 3 AND ELECTRICALINSULATION ACIDIC SMELL IN COCKPIT THEN THROUGHOUT CABIN WITH NO EVIDENCE OF SMOKE. THE SMELL DISSIPATED AFTER 15 MINUTES. THE RIGHT AUTOPILOT WAS ENGAGED WITH NO PROBLEM. FOUND THE CENTER FCC INOP WITH BURNING SMELL. REPLACED SAME. NO OTHER DEFECTS WERE FOUND. RAN MCDP TEST ON NEW FCC. ALL CHECKS WERE NORMAL OK FOR SERVICE